1. Field of the Invention
The invention relates to a device for filtering a light wave within a light-guiding fiber.
2. The Prior Art
Light-guiding fibers transmit optical information. In many cases, light waves in such fibers must for various reasons be subjected to polarization filtering or frequency-selective filtering. Such filtering is commonly performed before the light waves are fed into the fiber, or after transmission therethrough and after the light waves have been decoupled from the fiber. Because of space limitations, however, it is often desirable to filter a light wave without decoupling it from the end surface of the light-guiding fiber.
Thin-film filters are well known in the art such as from the German Offenlegungschrift No. 2,252,826. The Comte U.S. Pat. No. 3,436,141 discloses a hollow wave guide having a multiple layer cladding for selectively guiding only monochromatic light having a grazing incidence to the guide walls.